Thank you for posting your question here, I will try to answer it to the best of my abilities.
It can be that you are in the early stages of anemia
when symptoms havent sent in, thats why you havent noticed.
There are many reasons for anemia, the most simple would be your diet. Not eating enough iron or vitamin B12
. There are other causes as well, but usually these two are the more common ones.
Now the job of your doctor is to find the cause of your anemia, this will require a couple of tests. Once he is done with that, you can be treated accordingly.
I hope this answered your question.